Dissociation versus Hydration. 35 



are represented by five straight lines signify ? Nothing more 

 than that the values of s as a function of p can be represented 

 by five interpolation-formulas of the second degree with fifteen 

 arbitrary constants, of which MendelejefF uses only ten. From 

 the mathematical side, this presents nothing more astonishing 

 than that really this number of constants is necessary. There 

 is, we should think, scarcely an example to be found in expe- 

 rimental physics where such an analytical representation has 

 been considered satisfactory. The only conclusion to draw 

 from it is that a much better representation could probably be 

 found with a little trouble. All our modern experience goes 

 to show that we obtain much better results when, instead of 

 percentage composition, we take the number of gram- 

 molecules per litre as abscissas ; and therefore the latter mode 

 of representation is the more scientific. Were this much 

 more justifiable method of plotting adopted the straight lines 

 in the second figure would change into curves, and so the 

 whole foundation of the theory of hydrates would collapse. 



MendelejefF proposes, instead of the dissociation of the 

 electrolytes (MX for example) into ions, a dissociation of 

 MX. (k + l)H 2 into either MX.nH 2 and H 2 0, or into 

 M OH . mH 2 and HX . (n — m)H 2 (base and acid) to ex- 

 plain the quantity i(> 1). As he himself states, however, the 

 splitting-off of water would not give a sufficient explanation 

 of this fact. We must therefore take the other alternative, 

 that the electrolytes are partially decomposed into acid and 

 base. This decomposition is not conceivable for those electro- 

 lytes which are themselves acids or bases, for they could not 

 possibly be decomposed by the action of water. Yet HC1 

 and NaOH have values of i greater than unity. For salts, 

 however, it is at least conceivable. But then we should have 

 to assume that KC1 in normal solution had decomposed to the 

 extent of 75 per cent, into KOH and HC1. Now HC1 dif- 

 fuses considerably faster than KOH ; so that if KC1 solution 

 were brought into contact with water the latter would become 

 acid from HC1, and the solution alkaline from the KOH 

 remaining behind, just as happens with FeCl 3 . This is, how- 

 ever, in direct contradiction to all experience, as is every 

 assumption of dissociation (such as Planck has proposed) 

 where the parts with greater velocity do not exercise a strong 

 attraction on those with less, as is the case with electrically 

 charged ions. The view of electrolytic dissociation, on the 

 other hand, is so far from being in contradiction to the facts 

 of diffusion, that the values of the constants of diffusion can 

 be actually deduced from it (cf. Nernst, Zeitschr. fur pliysikal. 

 Chemie, ii« p. 627). It is surely a strange notion that the pro- 



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